It is well-known that the visible reflection of light rays from the surface of a sheet of glass may be reduced by modifying the surface of the glass sheet. For example, the surface of the glass sheet may be treated with an etchant such as hydrofluoric acid to produce a frosted, anti-reflective glass for use in portrait frames, etc. Another method for modifying the surface of a glass sheet to produce anti-reflective glass is by ion implantation, wherein ions of an element are electrically accelerated and injected into the glass sheet to a selected depth and concentration in order to produce a solid mixture in the surface region of the glass sheet which thereby exhibits a gradational refractive index.
Hines, R. L., "Radiation Effect of Positive Ion Bombardment on Glass, " Journal of Applied Physics, v. 28, no. 5, pp. 587-591 (1957) discloses the ion implantation of argon ions into the surface region of a soda-lime-silica glass sheet, to produce anti-reflective glass. Arnold, G. W., "Radiation Enhanced Diffusion in Ion-Implanted Glasses and Glass/Metal Couples," Mat. Res. Soc. Sym. Proc., v. 27, pp. 61-66 (1984) discloses that such ion implantation causes alkali atom migration to the surface of the soda-lime-silica glass sheet.
It has been discovered that glass sheets, whose surfaces have been modified by ion implantation to produce anti-reflective glass, lose their anti-reflective properties when the glass sheets are heated to conventional glass processing and fabricating temperatures, such as those used to provide pyrolytic coatings thereon or to heat and bend the glass sheets.
It would be desirable to develop a process for preparing ion implanted anti-reflective glass, which glass would not lose its anti-reflectivity as a result of being heated to conventional glass sheet fabricating and processing temperatures.